The civil engineering activities in the framework of the High Luminosity LHC project, the Geneva GEothermie 2020 and the continuous monitoring of the LHC civil infrastructures triggered the need for the installation of a seismic network at CERN. A 24 bits data acquisition system has been deployed in 3 places at CERN: ATLAS, CMS and the Prévessin site. The system is sending all the raw data to the Swiss Seismological Service and performs FFT on the fly to be stored in the LHC database. The system has shown a good sensitivity of 10-16 (m/s)2/Hz at 1 Hz.